Two-part drilling tool for the percussive or rotary percussive drilling of holes in soil material or rock material

ABSTRACT

In a two-part drilling tool for the percussive or rotary percussive drilling of holes in soil material or rock material, including a drill head ( 1 ) and an adapter part ( 7 ), which is fixed in an interior of the drill head ( 1 ) by way of interacting, complementary threads ( 11, 14 ) and is intended for providing the coupling to a drill string, wherein an end face ( 3 ) of the drill head ( 1 ) that is remote from a borehole interior rests on a complementarily formed stop or support surface of the adapter part ( 7 ), the end face ( 3 ) of the drill head ( 1 ) that is remote from the borehole interior and the stop or support surface of the adapter part ( 7 ) interacting therewith comprise complementarily formed wedge-shaped surfaces ( 4, 6 ) with end teeth ( 5, 8 ), and a lead angle (α 1 ) of the wedge-shaped surfaces ( 4, 6 ) is smaller than a lead angle (α 2 ) of an internal thread of the drill head ( 1 ) or the external thread interacting therewith of the adapter part ( 7 ) or of the drill string.

The present invention relates to a two-part drilling tool for the percussive or rotary percussive drilling of holes in soil material or rock material, including a drill head and an adapter part, which is fixed in an interior of the drill head by way of interacting, complementary threads and is intended for providing the coupling to a drill string, wherein an end face of the drill head that is remote from a borehole interior rests on a complementarily formed stop or support surface of the adapter part.

Drilling tools for the percussive or rotary-percussive drilling of holes in soil or rock material are known in various configurations and for the most diverse purposes of use, wherein, in recent times, drill bits have frequently been employed, part of which, i.e. the so-called ring drill bit, will remain in the borehole after completion of the latter, or so-called lost drill bits have been used, which will completely remain in the borehole upon completion thereof. For economic reasons, a relatively soft material is usually used for such drill bits either for the whole, or for at least part of, the ring drill bit, which will frequently entail problems when detaching and retracting the drill string, or an adapter connected to the drill string, upon completion of a borehole due to material deformations in the region of the connection of the drill head, or the drill bit, and the adapter or the rock-side end of the drill string. In order to minimize or completely avoid such deformations, various types of connections such as those described, for instance, in DE-A 25 43 578 or U.S. Pat. No. 2,052,011 have already been described, yet none of those connections provide sufficient lifetimes during percussive or rotary-percussive drilling.

From DE-A 33 30 025, a two-part, threaded drill is known, by which attempts have been made to keep free of bending moments the threaded connection of a drill with a drill string, and hence prevent the destruction of the thread, by providing stop or support elements having larger diameters than the threaded connection.

From GB 2 127 436 A, a two-part drill bit has become known, in which a drill head interacts with an adapter inserted in the drill bit via a thread, wherein the two parts comprise mutually different threads that are designed to safely absorb bending moments during drilling.

From EP-B 0 771 934, a drilling tool, in particular for working rock, has become known, in which the axial resilience of the thread is increased, and the susceptibility to wear of the latter is reduced, by the special configuration of a threaded connection between the drill head and the drill shaft.

The invention aims to provide a threaded connection between a lost drill bit, or a drill head, and an adapter, which ensures both a sufficient lifetime for the formation of a borehole and, upon completion of the drilling procedure, can be reliably detached in order to enable the safe and reliable recovery of reusable elements such as the drill rod and/or an adapter including a drill rod fixed thereto.

To solve this object, the two-part drilling tool according to the invention is characterized in that the end face of the drill head that is remote from the borehole interior and the stop or support surface of the adapter part interacting therewith are configured as complementarily formed wedge-shaped surfaces with end teeth, wherein, in the main, the wedge-shaped surfaces take up the impact stress and the end faces take up the torques, and that the lead angle of the wedge-shaped surfaces is smaller than the lead angle of the internal thread of the drill head, or the external thread interacting therewith of the adapter part. In that the drill head end face facing away from the interior of the borehole and the stop or support surface of the adapter part interacting with the former are designed as complementarily formed wedge-shaped surfaces with end teeth, an anti-twist protection of the complementary internal and external threads is provided, thus ensuring that excessive torque loads on the thread will be prevented. In that, furthermore, the lead angle of the wedge-shaped surfaces is smaller than the lead angle of the internal thread of the drill head, or the external thread of the adapter part interacting therewith, the relief of the thread in the axial direction will be safeguarded, since the impact stress will above all be applied to the wedge-shaped surfaces, and the surfaces of the interacting threads that are particularly vulnerable to excessive wear, namely the surface of the thread facing the mine interior on the adapter and the surface facing the mine exterior of the drill bit, or the drill head, respectively, will be substantially kept free from any impact stress in the axial direction.

Such a configuration will further ensure the adapter to be safely and reliably detached from the drill bit upon completion of a drilling procedure so as to avoid excessive material expenditures and, in particular, the loss of the adapter.

According to a preferred further development of the invention, the two-part drilling tool is configured such that the lead angle of the wedge-shaped surfaces is at least 10% and at most 50%, in particular about 25%, smaller than the lead angle of the internal and external threads. Due to a markedly reduced lead angle of the wedge-shaped surface relative to that of the internal thread of the drill head and the external thread of the adapter, lifts automatically the drill head when screwing the adapter into the drill head so as to automatically provide a certain play of the thread of the adapter in the internal thread of the drill head, thus keeping the threaded connection between the drill head and the adapter substantially free from axial forces during a drilling procedure.

In order to further reduce the axial load of the threads of the drill head and the adapter, the invention is preferably further developed such that thread roots of the complementary threads of the drill head and the adapter each extending in the axial direction of the two-part drilling tool in the axial direction of the two-part drilling tool have dimensions exceeding those of the thread heads. In that the thread root each has a larger longitudinal extension in the axial direction of the two-part drilling tool than the respective thread head engaging the thread root, the respective thread head will be kept completely free from axial loads whenever stress is exerted on the two-part drilling tool, and it will thereby be prevented that the complementary threads and, in particular, the internal thread of the drill head, which is usually made of a softer material, will be knocked out or rounded off by excessive loads during the drilling procedure and will no longer be detachable upon completion of the drilling procedure.

In that, as in correspondence with a preferred further development of the invention, the thread root exceeds the dimension of the thread head in the axial direction of the two-part drilling tool by at least one third of the height of the end teeth, not only the keeping-free of the complementary threads of any axial load will be ensured, but it will also be safeguarded that the free space between the thread head and the thread root will be sufficiently small so as not to be subjected to undesired bending moments during the drilling procedure and, be additionally contaminated by introduced rock residues to such an extent as to render impossible the detachment upon completion of the drilling procedure.

In order to ensure both the safe and reliable transmission of the impact energy to the drill head and the safe and reliable transmission of the rotational load on the drill head, the invention is preferably devised such that the end faces of the adapter and the stop or support surface of the drill head each comprise at least one, in particular at least three, wedge-shaped surface(s) with end teeth. By configuring at least one, in particular three, interacting wedge-shaped surface(s) of the adapter with the respectively complementary wedge-shaped surfaces of the drill head, the reliable transmission of the impact energy on the drill head will be feasible without stressing the threads of the drill head and the adapter in the axial direction.

By simultaneously providing end teeth abutting on one another in the case of engagement or during the drilling procedure, the safe transmission of the rotational movement of the drill string on the drill head will, on the one hand, be feasible and, on the other hand, securement against screwing the adapter too far into the drill head will be provided. The slope of the wedge-shaped surfaces in this case is selected such that the resulting longitudinal extension of the end teeth in the axial direction is so large that even with the highest rotating loads, or highest bending moments, sufficiently large support surfaces of end teeth formed on the drill head and on the adapter will be provided so as to ensure the safe and reliable transmission of the necessary torques while, at the same time, prevent excessive wear of the end teeth.

In that, as in correspondence with a preferred further development of the two-part drilling tool according to the invention, at least the wedge-shaped surfaces of the adapter are case-hardened, it will be safeguarded that the wedge-shaped surfaces, which are especially stressed and transmit the impact energy, will be secured against knocking-out and wearing. In that, in particular, the wedge-shaped surfaces of the adapter are case-hardened, the reutilization of this or these element(s) upon completion of a drilling procedure in subsequent drilling procedures will be ensured. In that, as in correspondence with a preferred further development of the invention, the wedge-shaped surfaces and the end teeth of the adapter are case-hardened, any highly-stressed elements of the adapter will be secured against premature wear. In that also the end teeth are case-hardened, not only the transmission of very high torques will be ensured but, above all, also the knocking-out of the extremely loaded regions of the end teeth will be avoided.

In order to further reduce load moments in the region of the end teeth and, in particular, prevent them from tearing out, the configuration according to the invention is preferably further developed such that approximately semicircular recesses are each formed in the region of the end teeth, both in the adapter and in the stop or support surface of the drill head. By forming said semicircular recesses, the formation of cracks, in particular under an excessive load of the extremely stressed regions of the end teeth, will be avoided by the introduced energy being distributed to the substantially semicircular recesses, thus also safely preventing the end teeth from tearing out or tearing off.

In order to ensure the safe detachment of the threaded connection between the drill head and the adapter, the two-part drilling tool according to the invention is preferably further developed such that the internal thread of the drill head and the complementary external thread of the adapter interacting therewith are designed as single-flight threads. By providing single-flight threads, it will be possible, even in the event of extreme contaminations and, for instance, the introduction of viscous or solidifying drilling mud, to safely detach the thread upon completion of the drilling procedure, and hence safely and reliably remove from the lost drill bit the elements intended for further use, namely the drill string and optionally an adapter for fixing the drill string.

In that the two-part drilling tool according to the invention, according to a preferred further development is, moreover, configured such that the respective turns of the threads of the drill head and the adapter extend over at least 75% and at most 99% of the circumferences of the adapter and the drill head, a safe connection of the drill head with the adapter will, on the one hand, be ensured, and it will, on the other hand, be safe-guarded that said connection will be reliably detachable even after extreme loads and/or contaminations.

A particularly simple and, at the same time, reliable screw-connection of the drill head with the adapter will be ensured, if, as in correspondence with a preferred configuration of the two-part drilling tool according to the invention, the complementary threads are designed as flat threads or trapezoidal threads having flank angles smaller than 25°. Flat threads or trapezoidal threads in a manner known per se are able to absorb high axial loads, and, on the other hand, will provide the play or free space that is required between a thread root and a respectively meshing thread head, in order to achieve the preferred characteristic features sought by the invention.

In the following, the invention will be explained in more detail by way of exemplary embodiments illustrated in the drawing. Therein:

FIG. 1 is an external view of a two-part drilling tool according to the invention in the position during the percussive or rotary-percussive drilling of holes in soil or rock material;

FIG. 2 depicts a longitudinal section along line A-A of FIG. 1, of the two-part drilling tool according to FIG. 1;

FIG. 3 is an enlarged view of the detail B of FIG. 2, indicating the alternate positions of the internal thread of the drill head and the external thread of the adapter in the state during drilling;

FIG. 4 again depicts a longitudinal section through the two-part drilling tool, said two-part drilling tool being illustrated in the position during the screwing of the adapter into the drill head;

FIG. 5 depicts a longitudinal section through the two-part drilling tool according to the invention in the operating state during the retraction of the drill string and the rotation of the same to the left in order to perform the rotational movement of a drill head during rotary percussive drilling;

FIG. 6 is an external view of the two-part drilling tool in the position according to FIG. 5; and

FIG. 7 illustrates a section through the adapter, showing the lead angles of the wedge-shaped surfaces and the thread, respectively.

FIG. 1 illustrates a drill head 1, in particular a so-called lost drill bit 1, which is formed with wedge-shaped surfaces 4 and end teeth 5 on its end side 3 that faces away from the excavation tools 2. The wedge-shaped surfaces 4 are configured to be in abutment on complementary wedge-shaped surfaces 6 of an adapter 7 during the drilling of holes in soil and/or rock materials, and via which wedge-shaped surfaces 4 and 6 the impact energy is applied to the drill head 1 via the adapter 7. The adapter 7 in addition to the wedge-shaped surfaces 6 comprises end teeth 8, which abut on the complementary end teeth 5 of the drill head 1 during drilling and, in particular, during the application of a torque during rotary percussion drilling, and which absorb, and withstand, torques applied to the two-part drilling tool.

In order to safely prevent the tearing out and, in particular, inadvertent deformation of the end teeth 5 and 8, substantially semicircular recesses 9 and 10 are respectively formed in the drill head 1 and in the adapter 7, which serve to take up excessive loads and to distribute the introduced energy, thus safely preventing the tearing off or knocking-out of the end teeth 5 and 8.

In FIG. 2, which shows a section along line A-A of FIG. 1, the reference numerals of FIG. 1 have been retained. In the interior of the drill bit 1, a single-flight thread 11 is formed, which is configured such that a thread root 12 has a larger longitudinal extension in the axial direction of the two-part drilling tool than a thread head 13 interacting with said thread root 12, of the thread 14 of the adapter 7, which engages the thread 11. The complementary thread 14 of the adapter 7 is likewise configured such that a thread root 20 has a larger axial longitudinal extension than a thread head engaging said thread root 20. Due to such a configuration, the interacting threads 11 and 14 substantially serve to center the adapter 7 in the drill head 1 and, in the event of load exerted on the drill head 1, particularly during percussion or rotary percussion drilling, will not absorb any axial load so as to be free of any loads acting in the axial direction. As can be taken from the enlarged partial view of FIG. 3, the configuration in this case is devised such that, during drilling, a thread head 13 of the thread 14 formed on the adapter 7 will be substantially centrally disposed in a thread root 12 of the complementary thread 11 within the drill head 1, and that substantially identical free spaces 15 will be provided on the two sides of the thread head 13, both in the direction towards the work face and the drill pins 2 of the drill head 1 and in the direction facing away from the borehole interior, such that no load whatsoever will act on the thread head(s) 13 during drilling and, in particular, percussion and/or rotary percussion drilling.

The interacting threads 11 and 14 in this case, in particular, ensure that the drill head 1 is centrally disposed on the adapter 7 and no bending elements will act on the drill bit during drilling.

Due to the configuration comprising the interacting wedge-shaped surfaces 4 of the drill bit 1, and 6 of the adapter 7, the safe and reliable transmission of the axial force of the drill string to the drill bit 1 will be safeguarded, and due to the configuration of the end teeth 5 and 8, respectively, the safe and reliable transmission of the torque to the drill bit 1 will, furthermore, be ensured during rotary percussion drilling.

In the illustration according to FIG. 4, in which the reference numerals of the preceding Figures have again been retained, the situation of the two-part drilling tool during the screwing of the adapter 7 into the drill head 1 is shown. During the screwing of the adapter 7 into the drill head 1, the forward end edge 16 of the thread head 13 of the thread 14 of the adapter 7 is positioned in abutment on the side cheek 17 of the thread root 12 of the internal thread 11 of the drill head 1, which side cheek is disposed in the direction towards the borehole interior, so as to ensure the safe centering of the adapter 7 in the interior of the drill head. The interacting wedge-shaped surfaces 5 and 6 of the drill head 1 and the adapter 7, respectively, in this case are configured such that they can be guided one above the other without impeding each other and also that the end teeth 5 and 8 respectively formed in the two elements 1 and 7 can be freely moved one above the other without colliding or hitting each other, thus ensuring the safe and reliable screwing of the adapter 7 into the drill head 1.

FIG. 5 finally depicts the two-part drilling tool during the retraction of the adapter 7 in the sense of arrow 17, as is usually performed during rotary percussion drilling. During the retraction of the adapter 7, the shoulder 18 of the thread head 13 of the thread 14 formed on the adapter 7, which shoulder faces away from the interior of the borehole, comes into abutment on the side 19 facing away from the interior of the borehole, of the thread 11 formed in the drill head 1 and, to be more precise, on the shoulder 19 facing away from the interior of the borehole, of the thread root 12 of the thread 11. In this position of the adapter 7 in the interior of the drill bit 1, the wedge-shaped surfaces 4 and 6 of the adapter 7 and the drill head 1, respectively, are lifted off each other, no longer directly abutting each other, and no axial load acts on the wedge-shaped surfaces 4 and 6. Yet, a sufficient level of overlapping of the end teeth 5 and 8 will remain, which overlapping will prevent an excessive torque load, which might possibly cause the end teeth 5 and 8 to break off, as can be seen from the illustration according to FIG. 6. From FIG. 6, it is additionally apparent that the end faces 4 and 6 do not engage each other and are lifted off each other such that no axial load takes place in the direction towards the borehole interior of the drill bit 1 through the adapter 7.

A configuration according to the present invention thus manages to provide a threaded connection 11, 14 between a drill head 1 and an adapter 7, which threaded connection 11, 14 is completely unloaded during drilling and by which connection the total axial load is applied to the drill head 1 via the wedge-shaped surfaces 4 and 6, and the torque load during rotary percussion drilling is applied via the end teeth 5 and 8, such that, overall, a wear of the thread 11 of the drill head 1 as well as the external thread 14 of the adapter 7 will be safely prevented, and the safe and reliable detachment of the drilling tool and the adapter 7 from the drill head 1 will be ensured upon completion of the drilling procedure, and even the adapter 7 will be available for further use.

FIG. 7, in which the reference numerals of the preceding Figures have been retained, depicts a section through an adapter 7, in which the lead angles α1 and α2 of the wedge-shaped surface 6 and the thread 14, respectively, are shown. The angles α1 and α2, which have been determined as lead angles of the respective threads based on a fictitious axis 22 extending normally to a longitudinal axis 21 of the adapter, clearly indicate that the screwing of the adapter 7 into the drill head 1, which is not illustrated in FIG. 7, forces the thread 14 to lift off the complementary thread 11 of the drill head 1, thus keeping the complementary threads 11, 14 free of forces in the axial direction during the drilling procedure.

The special constructive design, furthermore, ensures that the breaking-off of the end teeth 5 and 8 and a wear of the wedge-shaped surfaces 4 and 6 will be prevented, wherein, in particular, the wedge-shaped surfaces 6 and the end teeth 8 are case-hardened so as to achieve a particularly high stability. By forming the wedge-shaped surfaces 4 and 6 with leads that differ from those of the threads 11, 14 provided in the interior of the drill head 1 and on the exterior of the adapter 7, respectively, the threads 11, 14, in particular, will be kept free of loads in the axial direction, and hence not unnecessarily worn. 

1. A two-part drilling tool for the percussive or rotary percussive drilling of holes in soil material or rock material, including a drill head and an adapter part, which is fixed in an interior of the drill head by way of interacting, complementary threads and is intended for providing the coupling to a drill string, wherein an end face of the drill head that is remote from a borehole interior rests on a complementarily formed stop or support surface of the adapter part, characterized in that the end face of the drill head that is remote from the borehole interior and the stop or support surface of the adapter part interacting therewith are configured as complementarily formed wedge-shaped surfaces with end teeth, wherein, in the main, the wedge-shaped surfaces take up the impact stress and the end faces take up the torques, and that the lead angle of the wedge-shaped surfaces is smaller than the lead angle of the internal thread of the drill head, or the external thread interacting therewith of the adapter part.
 2. The two-part drilling tool according to claim 1, characterized in that the lead angle of the wedge-shaped surfaces is at least 10% and at most 50%, in particular about 25%, smaller than the lead angle of the internal and external threads.
 3. The two-part drilling tool according to claim 1, characterized in that thread roots of the complementary threads of the drill head and the adapter, or the drill rod, each extending in the axial direction of the two-part drilling tool in the axial direction of the two-part drilling tool have dimensions exceeding those of the thread heads.
 4. The two-part drilling tool according to claim 3, characterized in that the thread root exceeds the dimension of the thread head in the axial direction of the two-part drilling tool by at least one third of the height of the end teeth.
 5. The two-part drilling tool according to claim 1, characterized in that the end faces of the adapter and the stop or support surface of the drill head each comprise at least one, in particular at least three, wedge-shaped surface(s) with end teeth.
 6. The two-part drilling tool according to claim 1, characterized in that at least the wedge-shaped surfaces of the adapter are case-hardened.
 7. The two-part drilling tool according to claim 6, characterized in that the wedge-shaped surfaces and the end teeth of the adapter are case-hardened.
 8. The two-part drilling tool according to claim 1, characterized in that approximately semicircular recesses are each formed in the region of the end teeth, both in the adapter and in the stop or support surface of the drill head.
 9. The two-part drilling tool according to claim 1, characterized in that the internal thread and the complementary external thread interacting therewith are designed as single-flight threads.
 10. The two-part drilling tool according to claim 1, characterized in that the respective turns of the threads of the drill head and the adapter extend over at least 75% and at most 99% of the circumferences of the adapter and the drill head.
 11. The two-part drilling tool according to claim 10, characterized in that the complementary threads are designed as flat threads or trapezoidal threads having flank angles smaller than 25°. 